Disk Array Controller for Data Storage System
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^ ^ ^ ^ I ^ ^ ^ ^ II ^ II ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ I ^ � European Patent Office Office europeen des brevets £P Q 508 604 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) |nt CI.6: G06F 3/06, G06F 13/42, of the grant of the patent: G06F 11/10 17.11.1999 Bulletin 1999/46 (21) Application number: 92302098.6 (22) Date of filing: 11.03.1992 (54) Disk array controller for data storage system Speicherplattenanordnungsteuerungsvorrichtung fur eine Datenspeicherungsanordnung Dispositif de commande d'un reseau de disques pour un systeme de stockage de donnees (84) Designated Contracting States: • McCombs, Craig C. DE FR GB Wichita, KS 6721 3 (US) • Thompson, Kenneth J. (30) Priority: 13.03.1991 US 668660 Wichita, KS 67226 (US) (43) Date of publication of application: (74) Representative: Gill, David Alan et al 14.10.1992 Bulletin 1992/42 W.P. Thompson & Co., Celcon House, (73) Proprietors: 289-293 High Holborn • NCR International, Inc. London WC1V7HU (GB) Dayton, Ohio 45479 (US) • HYUNDAI ELECTRONICS AMERICA (56) References cited: Milpitas, California 95035 (US) EP-A- 0 294 287 EP-A- 0 320 107 • Symbios, Inc. EP-A- 0 369 707 US-A- 4 899 342 Fort Collins, Colorado 80525 (US) US-A-4 914 656 (72) Inventors: • Jibbe, Mahmoud K. Wichita, KS 67208 (US) DO ^- o CO 00 o 10 Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU Printed by Jouve, 75001 PARIS (FR) 1 EP 0 508 604 B1 2 Description paritydisk. In asimilarfashion, read operations typically need only access a single one of the N data disks, un- [0001] This invention relates to data storage systems less the data to be read exceeds the block length stored of the kind including host bus means adapted to be con- on each disk. As with RAID level 3 systems, the parity nected to a host device, and disk drive means adapted 5 disk is used to reconstruct information in the event of a to be connected to a plurality of disk drive devices. disk failure. [0002] Recent and continuing increases in computer [0007] RAID level 5 is similar to RAID level 4 except processing power and speed, in the speed and capacity that parity information, in addition to the data, is distrib- of primary memory, and in the size and complexity of uted across the N+1 disks in each group. Although each computer software has resulted in the need for faster 10 group contains N+1 disks, each disk includes some operating, larger capacity secondary memory storage blocks for storing data and some blocks for storing parity devices; magnetic disks forming the most common ex- information. Where parity information is stored is con- ternal or secondary memory storage means utilized in trolled by an algorithm implemented by the user. As in present day computer systems. Unfortunately, the rate RAID level 4 systems, RAID level 5 writes require ac- of improvement in the performance of large magnetic 15 cess to at least two disks; however, no longer does every disks has not kept pace with processor and main mem- write to a group require access to the same dedicated ory performance improvements. However, significant parity disk, as in RAID level 4 systems. This feature pro- secondary memory storage performance and cost im- vides the opportunity to perform concurrent write oper- provements may be obtained by the replacement of sin- ations. gle large expensive disk drives with a multiplicity of 20 [0008] In a known disk array system the host operates small, inexpensive disk drives interconnected in a par- as the RAID controller and performs the parity genera- allel array, which to the host appears as a single large tion and checking. Having the host computer parity is fast disk. expensive in host processing overhead. Furthermore, [0003] Several disk array design alternatives were the known system includes a fixed data path structure presented in an article titled "A Case for Redundant Ar- 25 interconnecting the plurality of disk drives with the host rays of Inexpensive Disks (RAID)" by David A. Patter- system. Rearrangement of the disk array system to ac- son, Garth Gibson and Randy H. Katz; University of Cal- commodate different quantities of disk drives or different ifornia Report No. UCB/CSD 87/391, December 1987. RAID configurations is not easily accomplished. This article discusses disk arrays and the improvements [0009] US-A-4,91 4,656 discloses a data storage sys- in performance, reliability, power consumption and scal- 30 tern including a host bus means adapted to be connect- ability that disk arrays provide in comparison to single ed to a host device, disk drive means adapted to be con- large magnetic disks. nected to a plurality of disk drive devices, selectively [0004] Five disk array arrangements, referred to as controllable coupling means connected to the host bus RAID levels, are described in the article. The first level means and to a plurality of buses and which includes RAID comprises N disks for storing data and N addition- 35 connecting means adapted to connect the host bus al "mirror" disks for storing copies of the information writ- means to a first group of buses. EP-A-0,369,707 dis- ten to the data disks. RAID level 1 write functions require closes a data storage system likewise including a host that data be written to two disks, the second "mirror" disk bus means for connection to a host device, disk drive receiving the same information provided to the first disk. means for connection to a plurality of disk drive devices When data is read, it can be read from either disk. 40 and selectively controllable coupling means connected [0005] RAID level 3 systems comprise one or more to the host bus means and the disk drive means. groups of N+1 disks. Within each group, N disks are [0010] EP-A-0,294,287and EP-A-0,320,107 relate to used to store data, and the additional disk is utilized to data storage systems of the type defined within the store parity information. During RAID level 3 write func- present application but all of these aforementioned sys- tions, each block of data is divided into N portions for 45 terns are disadvantageously restricted having regard to storage among the N data disks. The corresponding their adaptability and versatility for controlling data flow parity information is written to a dedicated parity disk. between a host and a disk array. When data is read, all N data disks must be accessed. [0011] It is an object of the present invention to pro- The parity disk is used to reconstruct information in the vide a data storage system of the kind specified which event of a disk failure. so may be readily adapted to support various disk drive ar- [0006] RAID level 4 systems are also comprised of ray configurations. one or more groups of N+1 disks wherein N disks are [0012] Therefore, according to the present invention, used to store data, and the additional disk is utilized to there is provided a data storage system, including host store parity information. RAID level 4 systems differ from bus means adapted to be connected to a host device, RAID level 3 systems in that data to be saved is divided 55 disk drive means adapted to be connected to a plurality into larger portions, consisting of one or many blocks of of disk drive devices, selectively controllable coupling data, for storage among the disks. Writes still require means connected to said host bus means and to a plu- access to two disks, i.e., one of the N data disks and the rality of array buses coupled to said disk drive means, 2 3 EP 0 508 604 B1 4 first connecting means adapted to connect said host bus bit line. Bus 16 includes 18 data lines, two of which are means to a first group of selected array buses charac- bus parity lines. Additional control, acknowledge and terized in that said first connecting means includes a plu- message lines, not shown, are also included with the rality of register means each associated with a respec- data busses. tive array bus and connected to said host bus means for 5 [0016] SCSI adapter 14, SCSI bus interface chips 31 receiving data therefrom, each register means having a through 36, SRAM 36 and microprocessor 51 are com- respective bus driver connected thereto and also con- mercially available items. For example, SCSI adapter nected to the associated array bus, the bus drivers being 1 4 may be a Fast SCSI 2 chip, SCSI bus interface chips selectively controllable to connect said host bus means 31 through 35 may be NCR 53C96 chips and microproc- to said first group of selected array buses, and in that 10 essor 51 could be a Motorola MC68020, 16 megahertz said coupling means includes parity generation means, microprocessor. Also residing on the microprocessor second connecting means adapted to connect a second bus are a one megabyte DRAM, a 1 28 kilobyte EPROM, group of selected array buses to the input of said parity an eight kilobyte EEPROM, a 68901 multifunction pe- generation means, and third connecting means adapted ripheral controller and various registers. to connect the output of said parity generation means to is [0017] SCSI data path chip 10 is an application spe- a third group of selected array buses.